which for portrait: 85mm1.8G vs 70-200mmF4?

All this recent talk about the 58mm and bokeh has turned my attention toward portraits and/or other shallow DOF work. I have the 70-200mm F/4 but not the 85mm1.8G. I was curious if the 70-200mm used at the 200mm @ F4 would give comparable bokeh to the 85mm @ f1.8.

Reason I why ask is because I also have the 24-120F4 and the 105mm F2.8D micro so it's a focal length that I'm well covered at. I just want to know if getting the wider aperture is worth it.